Image forming apparatus that varies size of transmission aperture for light from light emitter of sheet sensor, by rotating each of two actuators each having slit

ABSTRACT

A sheet feeding device includes a sheet table, a sheet sensor, a first actuator including a contact portion and a first screen, and a second actuator including an effector and a second screen. The first actuator rotates in a second direction when the contact portion is lifted by a sheet, and rotates in a first direction when the contact portion falls into a hole. The second actuator rotates in the second direction such that the second slit overlaps with the first slit, when the effector is subjected to pressure of the sheet. The first slit is formed so as to differ a size of an aperture, depending on whether the contact portion is in contact with the sheet, or in the hole. The second slit is formed so as to reduce the size of the aperture compared with when the effector is free from the pressure.

INCORPORATION BY REFERENCE

This application claims priority to Japanese Patent Application No. 2022-039506 filed on Mar. 14, 2022, the entire contents of which are incorporated by reference herein.

BACKGROUND

The present disclosure relates to an image forming apparatus having a paper cassette for storing sheets.

In general, existing image forming apparatuses, such as a copier or a multifunction peripheral, are configured to notify the user about a trouble, for example when sheets in a paper cassette have run out, or when paper jam has occurred.

SUMMARY

The disclosure proposes further improvement of the foregoing techniques.

In an aspect, the disclosure provides an image forming apparatus including an image forming device, a sheet feeding device, and a control device. The image forming device forms an image on a sheet. The sheet feeding device supplies the sheet to the image forming device. The control device includes a processor, and acts as a controller that controls an operation of the sheet feeding device, when the processor executes a control program. The sheet feeding device includes a sheet table, a sheet sensor, a first actuator, and a second actuator. The sheet table is supported on an upstream side in a sheet feeding direction so as to pivot in an up-down direction, and has a groove or a hole. The sheet sensor includes a light emitter, and a photodetector opposed thereto. The first actuator includes a first rotary shaft configured to rotate, an contact portion extending from the first rotary shaft toward the sheet table, and configured to be abutted against the sheet on the sheet table located at a predetermined standby position, by being biased in a predetermined first rotation direction about the first rotary shaft, and a first screen extending from the first rotary shaft to a space between the light emitter and the photodetector, and including a first slit. The second actuator includes a second rotary shaft coaxial with the first rotary shaft, and configured to rotate independent from the first rotary shaft, an effector extending from the second rotary shaft toward a sheet feeding path, and configured to contact the sheet feeding path by being biased in the first rotation direction, and a second screen extending from the second rotary shaft to a space between the light emitter and the photodetector, and including a second slit. When causing the sheet feeding device to feed the sheet, the controller locates the sheet table at a predetermined sheet feeding position, by causing the sheet table to pivot upward from the standby position. The first actuator rotates in a second rotation direction, opposite to the first rotation direction about the first rotary shaft, when the contact portion is lifted up by the sheet on the sheet table because of the sheet table being located at the sheet feeding position, and rotates in the first rotation direction, when the contact portion falls into the groove or the hole because of the sheet on the sheet table having run out. The second actuator is located such that the second screen keeps from blocking light emitted from the light emitter, when the sheet is not proceeding along the sheet feeding path, and located such that the second slit overlaps with the first slit, by rotating in the second rotation direction about the second rotary shaft, when the effector is subjected to pressure of the sheet proceeding along the sheet feeding path. The first slit is formed such that a size of a transmission aperture for the light emitted from the light emitter varies, depending on whether the contact portion is in contact with the sheet on the sheet table, or in the groove or the hole. The second slit is formed so as to reduce, by overlapping with the first slit, the size of the transmission aperture, compared with a case where the effector is not subjected to the pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment of the disclosure;

FIG. 2 is a functional block diagram showing an essential internal configuration of the image forming apparatus;

FIG. 3A and FIG. 3B are schematic front views each showing a sheet feeding device;

FIG. 4A is a front view of a first actuator;

FIG. 4B is a perspective view of the first actuator;

FIG. 4C is a front view of a second actuator;

FIG. 4D is a perspective view of the second actuator;

FIG. 5 is a perspective view showing a sheet table;

FIG. 6A and FIG. 6B are schematic front views each showing a state of a sheet detection mechanism, assumed when no sheet is placed on a sheet table located at a standby position;

FIG. 7A and FIG. 7B are schematic front views each showing a state of the sheet detection mechanism, assumed when a sheet is placed on the sheet table located at the standby position;

FIG. 8A and FIG. 8B are schematic front views each showing a state of the sheet detection mechanism, assumed when no sheet is delivered from the sheet table located at a sheet feeding position;

FIG. 9A and FIG. 9B are schematic front views each showing a state of the sheet detection mechanism, assumed when a sheet is delivered from the sheet table located at the sheet feeding position; and

FIG. 10 is a flowchart showing an example of a sheet status deciding operation.

DETAILED DESCRIPTION

Hereafter, an image forming apparatus according to an embodiment of the disclosure will be described, with reference to the drawings. FIG. 1 is a perspective view showing the appearance of the image forming apparatus 1 according to the embodiment of the disclosure. FIG. 2 is a functional block diagram showing an essential internal configuration of the image forming apparatus 1.

The image forming apparatus 1 is a multifunction peripheral having a plurality of functions, such as copying, printing, scanning, and facsimile transmission. The image forming apparatus 1 includes, inside the main body thereof, a control device 10, a document feeding device 6, a document reading device 5, an image forming device 12, a fixing device 13, a sheet feeding device 14, an operation device 47, and a storage device 8.

The document feeding device 6 is openably connected to the upper face of the document reading device 5, for example via a hinge. The document feeding device 6 serves as a document retention cover, when the document reading device 5 reads a source document placed on the platen glass. The document feeding device 6 is an automatic document feeder, abbreviated as ADF. The document feeding device 6 includes a document tray 61, and delivers the source documents placed thereon to the document reading device 5, one by one.

To perform the document reading operation, the image forming apparatus 1 operates as follows. The document reading device 5 optically reads the image on the source document delivered from the document feeding device 6 to the document reading device 5, or placed on the platen glass, and generates image data. The image data generated by the document reading device 5 is stored, for example, in an image memory.

To perform the image forming operation, the image forming apparatus 1 operates as follows. The image forming device 12 forms a toner image on a sheet serving as a recording medium, and supplied from the sheet feeding device 14, on the basis of the image data generated through the document reading operation, image data stored in the image memory, or image data received from a computer connected via a network.

The fixing device 13 heats and presses the sheet on which the toner image has been formed by the image forming device 12, to thereby fix the toner image on the sheet. The sheet that has undergone the fixing process is delivered to an output tray.

The sheet feeding device 14 serves to supply the sheets to the image forming device 12. The sheet feeding device 14 includes a plurality of paper cassettes 141A, 141B (hereinafter, simply “paper cassette 141” where appropriate) for storing the sheets. The paper cassette 141 includes a sheet feeding roller 32 (see FIG. 3A and FIG. 3B) for supplying the sheets stored therein to the image forming device 12, and a sheet sensor 34 for detecting the sheet stored in the paper cassette 141.

The operation device 47 receives the user's instructions to execute the functions and operations that the image forming apparatus 1 is configured to perform, such as the image forming operation. The operation device 47 includes a display device 473 for displaying, for example, an operation guide for the user. The operation device 47 receives, through a touch panel provided on the display device 473, the user's instruction based on an operation (touch operation) performed by the user on the operation screen displayed on the display device 473.

The operation device 47 also receives an input of the user's instruction, according to the user's operation performed on a physical key provided in the operation device 47.

The display device 473 includes, for example, a liquid crystal display (LCD). The display device 473 includes the touch panel. When the user touches a button or a key displayed on the screen, the touch panel receives the instruction corresponding to the touched position.

The storage device 8 is a large-capacity storage device such as a hard disk drive (HDD) and a solid state drive (SSD). The storage device 8 contains various control programs.

The control device 10 includes a processor, a random-access memory (RAM), a read-only memory (ROM), and an exclusive hardware circuit. The processor is, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), or a micro processing unit (MPU).

The control device 10 acts as a controller 100 and a decider 101, when the processor operates according to the control program stored in the storage device 8. Here, the controller 100 and the decider 101 may be constituted in the form of a hardware circuit, instead of being realized by the operation of the control device 10 according to the control program. This also applies to other embodiments, unless otherwise specifically noted.

The controller 100 serves to control the overall operation of the image forming apparatus 1. The controller 100 is connected to the document feeding device 6, the document reading device 5, the image forming device 12, the fixing device 13, the sheet feeding device 14, the operation device 47, and the storage device 8, and controls the operation of the mentioned components. For example, the controller 100 controls the operation of the image forming device 12, to form an image on the sheet delivered from the sheet feeding device 14.

The decider 101 decides the status of the sheet stored in the paper cassette 141, on the basis of a detection signal inputted by the sheet sensor 34.

FIG. 3A and FIG. 3B are schematic front views each showing the sheet feeding device 14. The sheet feeding device 14 includes the paper cassette 141 for accommodating sheets P therein. The paper cassette 141 includes a sheet table 31, the sheet feeding roller 32, a biasing mechanism, and a sheet detection mechanism 33. The sheet table 31 is configured to retain the sheets P stacked thereon. The sheet table 31 is supported on the upstream side in the sheet feeding direction, so as to pivot in the up-down direction. The sheet feeding roller 32 serves to feed the sheets P stacked on the sheet table 31 toward the image forming device 12 (see FIG. 1 ). The biasing mechanism biases the sheet table 31 upwardly.

In the sheet feeding device 14, the sheet table 31 is located at a predetermined standby position (bottom face of the paper cassette 141) as shown in FIG. 3A, when the sheet feeding roller 32 is not feeding the sheet P. When the sheet P is to be delivered by the sheet feeding roller 32, the controller 100 causes the sheet table 31 to pivot upward from the standby position, to a predetermined sheet feeding position (where the sheet P reaches the sheet feeding roller 32) as shown in FIG. 3B. The sheet feeding roller 32 feeds the uppermost one of the sheets P stacked on the sheet table 31 set at the sheet feeding position, to the image forming device 12.

The sheet detection mechanism 33 includes the sheet sensor 34, a first actuator 35, and a second actuator 36 (shaded section in FIG. 3A and FIG. 3B). The sheet sensor 34 includes a light emitter 341, and a photodetector 342 opposed thereto.

For example, a photo interrupter (PI) sensor may be employed as the sheet sensor 34. The light emitter 341 of the PI sensor is located on the far side in FIG. 3A and FIG. 3B. The photodetector 342 of the PI sensor is located on the near side in FIG. 3A and FIG. 3B.

The first actuator 35 includes a first rotary shaft 351, a contact portion 352, and a first screen 353. The first rotary shaft 351 is configured to rotate. The contact portion 352 extends from the first rotary shaft 351 toward the sheet table 31. The contact portion 352 is configured to pivot about the first rotary shaft 351. The contact portion 352 is configured to make contact with the uppermost one of the sheets P stacked on the sheet table 31. The first screen 353 extends from the first rotary shaft 351 to a space between the light emitter 341 and the photodetector 342. The first screen 353 is configured to pivot about the first rotary shaft 351. The first screen 353 moves between the light emitter 341 and the photodetector 342, thereby transmitting or blocking the light emitted from the light emitter 341.

The first rotary shaft 351 includes, for example, a coil spring. The first actuator 35 is biased in a first rotation direction toward the sheet table 31 (counterclockwise in FIG. 3A and FIG. 3B). Because of the first actuator 35 being biased in the first rotation direction about the first rotary shaft 351, the contact portion 352 makes contact with the sheet P on the sheet table 31 set at the predetermined standby position. In the first screen 353, a first slit 354 is formed to allow the light emitted from the light emitter 341 to pass through. The first slit 354 is formed in an arcuate shape of uneven width, about the axial center of the first rotary shaft 351 (or a line parallel to the axial center, and close thereto). In other words, the first slit 354 is formed in the arcuate shape having the radial center coinciding with the axial center of the first rotary shaft 351.

FIG. 4A is a front view of the first actuator 35. FIG. 4B is a perspective view of the first actuator 35. In the contact portion 352 of the first actuator 35, the portion connected to the first rotary shaft 351 is formed in a shape of 7. The shape of 7 defines a space SP for the sheet P to pass through.

FIG. 5 is a perspective view showing the sheet table 31. As shown in FIG. 5 , the sheet table 31 includes a hole 311, in which the contact portion 352 of the first actuator 35 is to fall, when no sheet P is placed on the sheet table 31. Here, a groove may be formed, instead of the hole 311.

When the contact portion 352 is lifted up by the sheet table 31, because the sheet table 31 having the sheet P thereon pivots upward and reaches the sheet feeding position, as shown in FIG. 3B, the first actuator 35 pivots in a second rotation direction (clockwise in FIG. 3A and FIG. 3B), opposite to the first rotation direction about the first rotary shaft 351. In contrast, when the contact portion 352 falls into the hole 311, because of the sheets P on the sheet table 31 having run out, the first actuator 35 pivots in the first rotation direction, about the first rotary shaft 351.

The second actuator 36 includes a second rotary shaft 361, an effector 362, and a second screen 363. The second rotary shaft 361 is coaxial with the first rotary shaft 351, and configured to rotate independent from the first rotary shaft 351. The effector 362 extends from the second rotary shaft 361 to the sheet feeding path for the sheet P. The effector 362 is configured to pivot about the second rotary shaft 361. A part of the effector 362 is located on the sheet feeding path for the sheet P, and is therefore subjected to the pressure from the sheet P proceeding along the sheet feeding path. The second screen 363 extends from the second rotary shaft 361 to the space between the light emitter 341 and the photodetector 342. The second screen 363 is configured to pivot about the second rotary shaft 361. The second screen 363 moves between the light emitter 341 and the photodetector 342, thereby transmitting or blocking the light emitted from the light emitter 341.

The second rotary shaft 361 includes, for example, a coil spring like the first rotary shaft 351. The second actuator 36 is biased in the first rotation direction (counterclockwise in FIG. 3A and FIG. 3B). Since the second actuator 36 is biased in the first rotation direction about the second rotary shaft 361, a part of the effector 362 makes contact with the sheet feeding path for the sheet P. In the second screen 363, a second slit 364 is formed to allow the light emitted from the light emitter 341 to pass through. The second slit 364 is formed in an arcuate shape of a constant width, about the axial center of the second rotary shaft 361 (or a line parallel to the axial center, and close thereto). In other words, the second slit 364 is formed in the arcuate shape having the radial center coinciding with the axial center of the second rotary shaft 361.

FIG. 4C is a front view of the second actuator 36. FIG. 4D is a perspective view of the second actuator 36.

When the effector 362 is not subjected to the pressure from the sheet P, the second actuator 36 is located at a position where the second screen 363 does not block the light emitted from the light emitter 341, as shown in FIG. 3A. In contrast, when the effector 362 is subjected to the pressure from the sheet P, the second actuator 36 pivots in the second rotation direction (clockwise in FIG. 3A and FIG. 3B) about the second rotary shaft 361, to a position where the second screen 363 blocks the light emitted from the light emitter 341, as shown in FIG. 3B.

FIG. 6A is a schematic front view showing a state of the sheet detection mechanism 33, assumed when no sheet P is placed on the sheet table 31 located at the standby position. FIG. 6B is a partially enlarged view from FIG. 6A. FIG. 6B illustrates a detection line 34L of the sheet sensor 34, instead of the sheet sensor 34 itself. This also applies to FIG. 7B to FIG. 9B, to be subsequently referred to. The detection line 34L extends in the radial direction of the first rotary shaft 351 and the second rotary shaft 361.

When the sheet table 31 is located at the standby position, and no sheet P is placed on the sheet table 31 as shown in FIG. 6A, the contact portion 352 falls into the hole 311 of the sheet table 31. Therefore, the first actuator 35 pivots about the first rotary shaft 351 in the first rotation direction (counterclockwise in FIG. 6A), and the contact portion 352 makes contact with the bottom face of the paper cassette 141. At this point, the second actuator 36 is located, as shown in FIG. 6B, such that the second screen 363 does not overlap with the detection line 34L (i.e., such that the second screen 363 does not block the light emitted from the light emitter 341).

However, the first slit 354 is not overlapping with the detection line 34L. Accordingly, the light emitted from the light emitter 341 is completely blocked by the first screen 353, and the light reception amount of the photodetector 342 becomes zero. Thus, the first slit 354 is formed in the first screen 353 so as not to overlap with the detection line 34L, when there is no sheet P on the sheet table 31 and therefore the contact portion 352 is caught in the hole 311 of the sheet table 31.

FIG. 7A is a schematic front view showing a state of the sheet detection mechanism 33, assumed when the sheet P is placed on the sheet table 31 located at the standby position. FIG. 7B is a partially enlarged view from FIG. 7A. As shown in FIG. 7A, when the sheet table 31 is located at the standby position, and the sheets P are stacked on the sheet table 31, the contact portion 352 makes contact with the uppermost one of the sheets P on the sheet table 31. Therefore, the first actuator 35 is slightly shifted from the position shown in FIG. 6A, in the second rotation direction (clockwise in FIG. 7A) about the first rotary shaft 351.

At this point, as shown in FIG. 7B, the second actuator 36 is located at the same position as in FIG. 6B, because the effector 362 is not subjected to the pressure from the sheet P. On the other hand, the first slit 354 is overlapping with the detection line 34L, and the size (width) of the transmission aperture for the light emitted from the light emitter 341 is W1. The width W1 corresponds to the width of the first slit 354.

As described above, the first slit 354 is formed in the first screen 353 such that, when the sheet table 31 is located at the standby position, the size (width) of the transmission aperture for the light emitted from the light emitter 341 becomes different, between when the contact portion 352 is in contact with the sheet P on the sheet table 31 (FIG. 7A), and when the contact portion 352 is caught in the hole 311 of the sheet table 31 (FIG. 6A).

In the case where the width of the first slit 354, overlapping with the detection line 34L when the contact portion 352 is caught in the hole 311 of the sheet table 31 (FIG. 6A), is defined as W0 for example, the first slit 354 is formed such that a relational expression as “width W1≠width W0” is established. In this embodiment, since the first slit 354 does not overlap with the detection line 34L, when the contact portion 352 is caught in the hole 311 of the sheet table 31 (FIG. 6A), the width W0 is zero.

FIG. 8A is a schematic front view showing a state of the sheet detection mechanism 33, assumed when no sheet P is delivered from the sheet table 31 located at the sheet feeding position. FIG. 8B is a partially enlarged view from FIG. 8A. When the sheet table 31 is located at the sheet feeding position as shown in FIG. 8A, the first actuator 35 shifted from the position shown in FIG. 7A, in the second rotation direction (clockwise in FIG. 8A) about the first rotary shaft 351.

At this point, since the effector 362 is not subjected to the pressure from the sheet P as shown in FIG. 8B, the second actuator 36 is at the same position as in FIG. 6B and FIG. 7B. On the other hand, the first slit 354 is overlapping with the detection line 34L, and therefore the size (width) of the transmission aperture for the light emitted from the light emitter 341 becomes W2. The width W2 corresponds to the width of the first slit 354.

FIG. 9A is a schematic front view showing a state of the sheet detection mechanism 33, assumed when the sheet P is delivered from the sheet table 31 located at the sheet feeding position. FIG. 9B is a partially enlarged view from FIG. 9A. When the effector 362 is subjected to the pressure from the sheet P proceeding along the sheet feeding path, as shown in FIG. 9B, the second actuator 36 is shifted from the position shown in FIG. 6B to FIG. 8B, in the second rotation direction (clockwise in FIG. 9B) about the second rotary shaft 361. However, as shown in FIG. 9A, the first actuator 35 is located at the same position as in FIG. 8A.

The second slit 364 overlaps with the first slit 354 on the detection line 34L as shown in FIG. 9B, thereby reducing the size (width) of the transmission aperture for the light emitted from the light emitter 341 to W3, from W2 (width of first slit 354).

Thus, the second slit 364 is formed in the second screen 363 so as to overlap with the first slit 354 on the detection line 34L, when the effector 362 is subjected to the pressure from the sheet P, thereby reducing the size of the light transmission aperture, compared with the case where the effector 362 is not subjected to the pressure. In this embodiment, since the second slit 364 is independent from the first screen 353 on the detection line 34L, the width of the second slit 364 corresponds to the width W3 of the light transmission aperture.

Hereunder, an example of the determination method of the widths W0 to W3, corresponding to the size of the light transmission aperture, will be described. When the maximum receivable light amount of the photodetector 342 is defined as 100%, the width W2 of the first slit 354 is determined such that the light reception amount becomes between 70% and 100%, both ends inclusive. The width W3 of the second slit 364 is determined such that the light reception amount becomes between 30% and 69%, both ends inclusive. The width W1 of the first slit 354 is determined such that the light reception amount becomes between 1% and 29%, both ends inclusive. The width W0 of the first slit 354 is determined as zero.

Hereunder, a sheet status deciding operation performed by the control device 10 of the image forming apparatus 1 will be described, with reference to a flowchart shown in FIG. 10 .

The controller 100 acquires the detection signal inputted by the sheet sensor 34 (step S1). The decider 101 decides whether the light reception amount of the photodetector 342 is equal to or higher than 70% of the maximum value (maximum receivable light amount), on the basis of the detection signal acquired by the controller 100 (step S2). Upon deciding that the light reception amount is equal to or higher than 70% (YES at step S2), the decider 101 decides that although the sheet table 31 is located at the sheet feeding position, the sheet P is not being supplied (see FIG. 8B) (step S3), and finishes the sheet status deciding operation.

Upon deciding that the light reception amount is not equal to or higher than 70% (NO at step S2), the decider 101 decides whether the light reception amount of the photodetector 342 is equal to or higher than 30% of the maximum value (step S4). Upon deciding that the light reception amount is equal to or higher than 30% (YES at step S4), the decider 101 decides that the sheet P is being supplied (see FIG. 9B) (step S5), and finishes the sheet status deciding operation.

Upon deciding that the light reception amount is not equal to or higher than 30% (NO at step S4), the decider 101 decides whether the light reception amount of the photodetector 342 is equal to or higher than 1% of the maximum value (step S6). Upon deciding that the light reception amount is equal to or higher than 1% (YES at step S6), the decider 101 decides that the sheet table 31 is located at the standby position, and that one or more sheets P are placed on the sheet table 31 (see FIG. 7B) (step S7), and finishes the sheet status deciding operation.

In contrast, upon deciding that the light reception amount is not equal to or higher than 1% (NO at step S6), the decider 101 decides that no sheet P is placed on the sheet table 31 (see FIG. 6B) (step S8), and finishes the sheet status deciding operation.

Now, the aforementioned existing image forming apparatuses are configured to detect whether the sheet is placed on the paper cassette, but not configured to detect paper jam. In general, an additional sensor such as a PI sensor has to be provided, in order to detect the paper jam. However, an increase in number of the sensors makes the harness design and also the structure of the device complicated.

According to the foregoing embodiment, in contrast, the size (width) of the light transmission aperture varies, between when the contact portion 352 is in contact with the sheet P on the sheet table 31 (with the sheet), and when the contact portion 352 is caught in the hole 311 of the sheet table 31 (no sheet). Accordingly, the light reception amount of the photodetector 342 varies, and therefore whether the sheet P is present can be decided, on the basis of the difference in light reception amount.

The second slit 364 is formed so as to overlap with the first slit 354, when the effector 362 is subjected to the pressure from the sheet P (when the sheet P is being supplied), thereby reducing the size (width) of the light transmission aperture, compared with the case where the effector 362 is not subjected to the pressure (when the sheet P is not being supplied). Accordingly, the light reception amount of the photodetector 342 varies, and therefore whether the sheet P is being normally supplied can be decided, on the basis of the difference in light reception amount.

When the sheet is being normally supplied, the sheet P does not stay at a specific position (where the sheet P presses the effector 362) for a long time. Accordingly, in the case where the sheet P stays at the specific position for a predetermined time (e.g., 10 seconds) or longer, it can be assumed that the sheet is not being normally supplied, and that the paper jam has occurred. Therefore, the decider 101 decides that the paper jam has occurred, when the presence of the sheet P at the specific position has been detected for the predetermined time or longer. Consequently, the decider 101 can detect the presence of the sheet P, and the occurrence of the paper jam, by utilizing the second actuator 36 and the sheet sensor 34, without the need to additionally provide the sensor exclusively for detecting the paper jam.

Now, the size (width) of the transmission aperture for the light emitted from the light emitter 341 is determined on the basis of the positional relation between the first screen 353 having the first slit 354, and the second screen 363 having the second slit 364.

The first screen 353 pivots about the first rotary shaft 351, and the second screen 363 pivots about the second rotary shaft 361, which is coaxial with the first rotary shaft 351. The first slit 354 and the second slit 364 are each formed in the arcuate shape, about the axial center of the first rotary shaft 351 and the second rotary shaft 361 (or a line parallel to the axial center, and close thereto). Therefore, it is on the straight line extending in the radial direction of the first rotary shaft 351 and the second rotary shaft 361, that the variation of the size of the light transmission aperture appears most prominently.

According to the foregoing embodiment, the detection line 34L of the sheet sensor 34 extends in the radial direction of the first rotary shaft 351 and the second rotary shaft 361. Thus, the sheet sensor 34 is located at the position where the variation of the size of the light transmission aperture (i.e., variation of the light reception amount of the photodetector 342) can be most notably observed, and therefore high detection accuracy of the variation can be attained. Here, in the case where the detection line extends along the arcuate shape, the light reception amount of the photodetector 342 remains unchanged, regardless that the size of the light transmission aperture varies.

Although the width W0 to the width W3 of the light transmission aperture are different from one another in the foregoing embodiment, the disclosure is not limited to such embodiment. The location of the sheet table 31 (standby position or sheet feeding position) can be easily identified on the basis of information other than the light reception amount of the photodetector 342, and therefore the advantage of the disclosure can be attained, provided that the width W0 is different from the width W1, and that the width W2 is different from the width W3.

The disclosure may be modified in various manners, without limitation to the foregoing embodiment. The configurations and processings described in the foregoing embodiment and variations with reference to FIG. 1 to FIG. 10 are merely exemplary, and in no way intended to limit the disclosure to those configurations and processings.

While the present disclosure has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art the various changes and modifications may be made therein within the scope defined by the appended claims. 

What is claimed is;:
 1. An image forming apparatus comprising: an image forming device that forms an image on a sheet; a sheet feeding device that supplies the sheet to the image forming device; and a control device including a processor, and configured to act as a controller that controls an operation of the sheet feeding device, when the processor executes a control program, wherein the sheet feeding device includes: a sheet table supported on an upstream side in a sheet feeding direction so as to pivot in an up-down direction, and having a groove or a hole; a sheet sensor including a light emitter, and a photodetector opposed thereto; a first actuator including a first rotary shaft configured to rotate; an contact portion extending from the first rotary shaft toward the sheet table, and configured to be abutted against the sheet on the sheet table located at a predetermined standby position, by being biased in a predetermined first rotation direction about the first rotary shaft; and a first screen extending from the first rotary shaft to a space between the light emitter and the photodetector, and including a first slit; and a second actuator including a second rotary shaft coaxial with the first rotary shaft, and configured to rotate independent from the first rotary shaft; an effector extending from the second rotary shaft toward a sheet feeding path, and configured to contact the sheet feeding path by being biased in the first rotation direction; and a second screen extending from the second rotary shaft to a space between the light emitter and the photodetector, and including a second slit, the controller locates the sheet table at a predetermined sheet feeding position, by causing the sheet table to pivot upward from the standby position, when causing the sheet feeding device to feed the sheet, the first actuator rotates in a second rotation direction, opposite to the first rotation direction about the first rotary shaft, when the contact portion is lifted up by the sheet on the sheet table because of the sheet table being located at the sheet feeding position, and rotates in the first rotation direction, when the contact portion falls into the groove or the hole because of the sheet on the sheet table having run out, the second actuator is located such that the second screen keeps from blocking light emitted from the light emitter, when the sheet is not proceeding along the sheet feeding path, and located such that the second slit overlaps with the first slit, by rotating in the second rotation direction about the second rotary shaft, when the effector is subjected to pressure of the sheet proceeding along the sheet feeding path, the first slit is formed such that a size of a transmission aperture for the light emitted from the light emitter varies, depending on whether the contact portion is in contact with the sheet on the sheet table, or in the groove or the hole, and the second slit is formed so as to reduce, by overlapping with the first slit, the size of the transmission aperture, compared with a case where the effector is not subjected to the pressure.
 2. The image forming apparatus according to claim 1, wherein the first slit and the second slit are formed in an arcuate shape having a radial center coinciding with an axial center of the first rotary shaft, and a detection line of the sheet sensor extends in a radial direction of the first rotary shaft.
 3. The image forming apparatus according to claim 1, wherein the first slit is formed in a shape that makes the size of the transmission aperture different, between when the sheet table is located at the standby position, and when the sheet table is located at the sheet feeding position.
 4. The image forming apparatus according to claim 3, wherein the first slit and the second slit are formed in a shape that makes the size of the transmission aperture different, between when the effector is subjected to the pressure, and when the sheet table is located at the standby position.
 5. The image forming apparatus according to claim 1, wherein the control device further acts as a decider that decides a status of the sheet, on a basis of a difference in light reception amount of the photodetector.
 6. The image forming apparatus according to claim 2, wherein the first slit is formed in the first screen, so as not to overlap with the detection line, when the contact portion is caught in the groove or the hole. 